If Gordon Brown is looking for the ultimate eco-friendly house, he could do worse than travel to Britain's most northerly island. Michael and Dorothy Rea's zero-carbon house on Unst, part of the Shetland Islands, has demonstrated the potentially enormous benefits of living “off grid” in a house that has no carbon “footprint” whatsoever.

Built on the site of a former cottage, it boasts maximum heat retention, has double-glazed windows filled with argon gas, and all-round insulation provided by 140mm of expanded foam. Power is supplied by a 2.5Kw wind turbine. Because the house is completely sealed, very little cold and moisture gets in, while only a minimum of heat is allowed to escape.

The house also makes use of a fuel cell which, along with a highly insulated 4,200-litre water tank, provides a heat reservoir for an air-to-water heat pump, which in turn powers an under-floor heating system.

Mr Rea has dismissed claims by some building firms that such an energy-efficient house would cost about £700,000 as “nonsense”, saying that his four-bedroom property, known as Auld Batavia, cost in the region of £210,000.

After falling in love with Unst while on holiday in 1983, the Reas, from Wiltshire, eventually moved to the island in 2001. The concept of the eco house came about after a meeting with Jeff Kenna, chief executive of energy for Sustainable Development, part of the Camco Group.

Together with Dr Kenna, the couple put together a proposal to the Carbon Trust for funding. However, Mr Rea said, this was turned down at the time for being, in the words of the Carbon Trust, “too innovative”.

The Reas then decided to seek private sponsorship. Companies proved only too willing to help, either financially or by providing discounted services, to get the house up and running. The project, and its associated website, is able to provide companies with a perfect platform to demonstrate the effectiveness of their products.

Mr Rea, 63, a product designer, said: “We wanted to show that you didn't need to spend a lot of money to build an energy-efficient house.” Although the £210,000 price does not take into account the home's wind turbine, Mr Rea insisted that heat retention is the key to saving money. “There is no great secret to making an energyefficient house,” he said. “The most important aspect is to insulate them all.”

In theory, the battery can store four days' worth of energy should the wind on Unst stop blowing, which does not happen all that often. Mr Rea said: “We have the most efficient wind speeds in the world, at 52 per cent.”

The project also incorporates heat recovery, which works by passing all the air within the house over time through a system that recovers around 90 per cent of the heat in it.

The house has created a great deal of interest worldwide, with the Reas receiving correspondence from as far afield as the United States and China. Mr Rea has recently been dealing with a Swedish architect keen to incorporate the Unst heating system into his own properties. He has also been invited by Scottish Renewables to address builders and architects at its annual conference in Aviemore next month.

“These are the people that we really need to get through to,” he said., “Being energy-efficient is not rocket science. Apart from the fuel cell, everything we use is available off the shelf.”

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